1. Field of the Invention
The present invention relates to a gas transfer pipe arrangement for transferring gas containing droplets of diameters no less than 8 .mu.m at a velocity no less than 6 m/sec, which is employed, for example, in the chemical plant.
2. Description of the Prior Art
In many plants in petroleum refining industries, petrochemical industries and the like, droplets may be generated in the gas flow during processing. Upon transferring the gas flow containing the droplets, it may be necessary, depending on process steps carried out at a destination of the transferred gas, to remove the droplets from the gas flow. For example, at an inlet port of a compressor in the LNG or ethylene plant, it is required to remove no less than 99.9% of droplets having diameters of no less than 8 .mu.m in view of the properties of gas. On the other hand, in a certain reaction system, it is necessary to suppress the amount of droplets contained in the gas flow as much as possible. For achieving this, a special installation, called a knockout drum, a compressor suction drum or the like, having a droplet separating function is provided between adjacent pipes so as to remove the droplets in the gas flow during transfer of the gas. Such a drum is independent of the pipes and detachably coupled to the adjacent pipes by fastening their flanges through bolts.
There have been available various types of droplet separators for such a use, for example, a gravity type in which droplets are separated through gravitational precipitation, a impingement type in which droplets are separated through impingement against a pad which, on the other hand, passes gas therethrough, an inertial force type in which droplets are separated through a difference in specific gravity between gas and droplets utilizing inertial forces, and a centrifugal force type in which droplets are separated through a difference in specific gravity between gas and droplets by applying a centrifugal force to droplets in the gas flow.
FIG. 13 shows an example of the impingement type. In this example, a mesh pad 12 is provided in a separator vessel 11 at an upper side thereof. In this droplet separator, gas containing droplets is introduced into the separator vessel 11 via a gas inlet port 13a provided substantially at the center of the side wall of the separator vessel 11 and flows upward toward a gas outlet port 13b provided at the top of the separator vessel 11 via the mesh pad 12. Upon passing the mesh pad 12, the droplets collide against the surfaces of the mesh pad 12 to gradually form liquid films which then drop due to the gravity to be separated from the gas flow and are then discharged via a liquid outlet port 14 provided at the bottom of the separator vessel 11.
FIG. 14 shows an example of the inertial force type. In this example, Impingement plates called vanes 16 each having, for example, a corrugated shape are arranged at regular intervals in a separator vessel 15. Each of the vanes 16 is disposed vertically and in parallel to a flow passage of gas. At upstream and downstream sides of a flow passage of the separator vessel 15, triangle pole-shaped flow passage members 18a and 18b are provided, respectively. A gas inlet port 17a and a gas outlet port 17b are arranged at an upstream end of the flow passage member 18a and at a downstream end of the flow passage member 18b, respectively. In this droplet separator, the gas containing droplets flows zigzag between the adjacent vanes 16. While flowing, inertial forces are applied to droplets having large specific gravities so that the droplets deviate from the flow line of the gas and collide against the surfaces of the vanes 16 to form liquid films so as to be separated from the gas flow. Then, the gas is discharged via the gas outlet port 17b, while the liquid is discharged via a liquid outlet port 19 provided at a lower side of the vanes 16.
In the foregoing droplet separator of any type, however, the gas velocity within the applicable range thereof is sometimes lower than the gas velocity in the pipe. Accordingly, for reliably achieving the removal of droplets, it is necessary to reduce the gas velocity so that the inner diameter of the separator vessel is required to be set significantly greater than that of the pipe. In the LNG or ethylene plant, since the inner diameter of the pipe is large, that is, some tens of centimeters to about lm, the droplet separator is much increased in size corresponding to the large-diameter pipe.
Therefore, the cost of the droplet separator itself is increased, and a corresponding large space therefore is required, and further the piping becomes complicate, resulting in cost increase on the whole. Further, since the size increase of the droplet separator causes the size increase of a device for collecting the droplets separated by the droplet separator, a lot of labor and time are required for maintenance, check and recovery.